1. Field of the Invention
The present invention relates to a single crystal pulling apparatus for producing a single crystal of a semiconductor such as silicon (Si) or gallium arsenide (GaAs) using a continuous charge magnetic field application CZ technique (hereafter abbreviated as the CMCZ technique), and in particular relates to a single continuous crystal pulling apparatus in which the influence exerted by the introduction of additional source material has been reduced.
2. Description of the Related Art
Single crystal pulling apparatus employing the CZ technique comprises a gas tight chamber, a crucible for storing a semiconductor melt which is positioned inside the chamber, a heater for heating the semiconductor melt, and a pulling mechanism for pulling a single crystal of the semiconductor. In this type of apparatus a seed crystal of the single crystal of the semiconductor is immersed in the semiconductor melt inside the crucible, and the seed crystal is then gradually pulled upwards, growing a large diameter single crystal of the semiconductor which has the same orientation as the seed crystal.
In recent years there has been considerable development of the CMCZ technique, which is a variety of the CZ technique, where continuous pulling is achieved by continuously supplying the source material to the crucible. The CMCZ technique employs an integrated double crucible comprising an inner crucible and an outer crucible which are connected at the lower edge, and a single crystal of the semiconductor is pulled from the inner crucible, while source material is added to the region of the semiconductor melt between the outer and inner crucibles through a source material supply tube made of quartz. The source material supply tube is suspended from the upper portion of the chamber, and the lower end of the tube is proximate to the surface of the semiconductor melt inside the outer crucible. In the CMCZ technique the source material added through the source material supply tube gradually melts in the semiconductor melt, and eventually passes through the connecting portion, which connects the outer and inner crucible at the lower edge of the inner crucible, and flows into the inner crucible, where it is pulled up as a single crystal of the semiconductor. Investigations into the cause of the occurrence of voids in single semiconductor crystals reveal that extensive diffusion into the semiconductor melt in the region of the source material addition will generate voids (referred to herein as a void generation source) and is one factor inhibiting the healthy growth of single crystals of a semiconductor. In particular, if the downward force of the added source material is large or the source material drops in lumps, the depth to which the source material penetrates the semiconductor melt is increased, and so the effects of diffusion of void generation sources are particularly marked.
The present invention takes the above situation into consideration, with the object of providing a single continuous crystal pulling apparatus which enables maximum reduction in the effects caused by diffusion of void generation sources due to source material addition, which is considered one of the major factors inhibiting the healthy growth of single crystals of semiconductors.